Genocide denial is when people say that a terrible thing called genocide never happened. Genocide is when a large group of people, like a tribe or a race, is systematically killed off by another group. It's like when someone wants to completely erase a certain group of people from the world.
Some people want to deny that these things happen because they don't want to feel guilty, they don't want to believe that people can be so cruel, or they want to protect the people who did it. But denying that a genocide happened makes it harder for people to understand why it happened and to try to prevent it from happening again in the future. It's important to remember and acknowledge the terrible things that have happened in the past, so we can work towards a better future where everyone is safe and valued.